～てしまう

RuleVerb te-form + shimau: completion, or regret/chagrin ("end up V-ing").

Curiosity

The relief of "I finished all the homework" and the regret of "I lost my wallet." How are both said in Japanese?

Intuition

shimau ("to finish/put away") turns an action into something "done completely." It covers both good completion (got it all done) and bad completion (irreversible). Context decides relief versus regret.

Visualization

taberu (eat) → tabete (te-form) → tabete shimau (end up eating). Casual: tabechau.

食べるdictionary form

Essence

Verb te-form + shimau (tabete shimau). Casual contractions: ~te shimau → ~chau, ~de shimau → ~jau (nonjau). The past ~te shimatta especially conveys regret (chikoku shite shimatta). For emphasized completion it echoes sukkari / zenbu.

Examples

宿題を全部やってしまいました。

I finished all the homework (got it all done).

電車に傘を忘れてしまった。

I ended up leaving my umbrella on the train.

ケーキを全部食べちゃった。

I ate up all the cake. (casual)

Mini-quiz

Which expresses "I (regrettably) forgot the promise"?